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Force equilibrium of a thick-walled pipe

  1. Dec 15, 2011 #1
    Dear all,

    I have a thick-walled pipe with an inner radius a and an outer radius b. The pipe is mounted to an outer rigid surrounding by N number of screws (applied at radius b) equally distributed around the pipe. Given an applied moment M on the inner radius a, I want to calculate the forces acting on the screws in order to verify that the screws are strong enough to keep the pipe in place.

    Would the force F on each screw in such situation simply be F = M/(N*b) ? That is by using momentum equilibirum M = N*b*F around the center of the pipe. Or would the material deformation change this equilibrium in any way?

    I would appreciate any help you may offer.

    All the best
     
  2. jcsd
  3. Dec 16, 2011 #2
    "F on each screw"...in which direction? I presume that the F that appears in F=M/(N*b) is the F tangential to the outside of the pipe and right where the bolt contacts the pipe...in other words, this is friction force (if negligible deformation); it would be the same force that is trying to "bend" the bolt, but it is different from the force along the axis of the bolt...am I correct? Where, of course, Ffirction = Faxial-bolt X Friction-Coeff. ?
     
  4. Dec 16, 2011 #3
    Thank you very much for your reply.

    I realize that I was quite unclear in my question. There is going to be bolted joints between the rigid surrounding and the pipe, where the screw threads are in the pipe. So with the force F, I was referring to the shear force that would act on one screw. In the case where any friction at the interface between the pipe and the surrounding can be neglected, I wondered if moment equilibrium would be the only factor I have to consider? Because that would simply give me F = M/(N*b). However, I am unsure if I need to account for the deformation of the pipe since the moment is acting on the inner surface.

    If I know the shear force together with the preload along the bolt axis, I can then go ahead and use for example von Mises yield criterion to determine how many screws of a specific type that are needed to hold the pipe in place without reaching the yield point of the screw material.
     
    Last edited: Dec 16, 2011
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